Microwave integrated quantum circuits with cap wafers and their methods of manufacture
In a general aspect, an integrated quantum circuit includes a first substrate and a second substrate. The first substrate includes a first surface and a recess formed in the first substrate along the first surface. The recess has a recess surface and is configured to enclose a quantum circuit element. The first substrate includes a first electrically-conductive layer disposed on the first surface and covering at least a portion of the recess surface. The first electrically-conductive layer includes a first superconducting material. The second substrate includes a second surface and a quantum circuit element. The second substrate includes a second electrically-conductive layer on the second surface that includes a second superconducting material. The first substrate is adjacent the second substrate to enclose the quantum circuit device within the recess. The first electrically-conductive layer of the first substrate is electrically-coupled to the second electrically-coupled layer of the second substrate.
1. A method of fabricating an integrated quantum circuit, the method comprising:
forming a recess in a first substrate along a first surface thereof, the recess having a recess surface and configured to enclose a quantum circuit device;
depositing a first electrically-conductive layer over the first surface of the first substrate and at least a portion of the recess surface, the first electrically-conductive layer comprising a first superconducting material;
depositing a second electrically-conductive layer over a second surface of a second substrate, the second electrically-conductive layer comprising a second superconducting material;
forming the quantum circuit device on the second substrate, the quantum circuit device disposed on and contacting the second surface of the second substrate; and
assembling the first substrate to the second substrate to:
enclose the quantum circuit device of the second substrate within the recess of the first substrate; and
electrically couple the first electrically-conductive layer with the second electrically-conductive layer.
2. The method of claim 1 , wherein depositing the first electrically-conductive layer comprises patterning the first electrically-conductive layer.
3. The method of claim 1 , wherein depositing the first electrically-conductive layer comprises depositing a plurality of layers to form a first multi-layer stack, at least one of the plurality of layers formed of the first superconducting material.
4. The method of claim 1 , wherein depositing the first electrically-conductive layer comprises:
depositing a first layer of niobium over the first surface of the first substrate and at least the portion of the recess surface, the niobium corresponding to the first superconducting material; and
depositing a layer of an alloy of molybdenum and rhenium over the first layer of niobium.
5. The method of claim 4 , comprising:
prior to depositing the layer of an alloy of molybdenum and rhenium,
depositing a layer of an alloy of titanium and tungsten over the first layer of niobium;
depositing a second layer of niobium over the layer of the alloy of titanium and tungsten; and
wherein the layer of the alloy of molybdenum and rhenium is deposited over the second layer of niobium.
6. The method of claim 1 , wherein depositing the second electrically-conductive layer comprises patterning the second electrically-conductive layer.
7. The method of claim 1 , wherein depositing the second electrically-conductive layer comprises depositing a plurality of layers to form a second multi-layer stack, at least one of the plurality of layers formed of the second superconducting material.
8. The method of claim 1 , wherein depositing the first electrically-conductive layer comprises:
depositing a layer of niobium over the second surface of the second substrate, the niobium corresponding to the second superconducting material; and
depositing a layer of an alloy of molybdenum and rhenium over the layer of niobium.
9. The method of claim 1 , comprising:
electrically-coupling the first electrically-conductive layer with the second electrically-conductive layer through a third superconducting material.
10. The method of claim 9 , wherein electrically-coupling the first electrically-conductive layer with the second electrically-conductive layer comprises:
depositing a patterned layer of the third superconducting material over the first electrically-conductive layer of the first substrate; and
contacting the patterned layer of the third superconducting material with the second electrically-conductive layer of the second substrate.
11. The method of claim 9 , wherein electrically-coupling the first electrically-conductive layer with the second electrically-conductive layer comprises:
coupling a bump of the third superconducting material to the first electrically-conductive layer of the first substrate; and
contacting the bump of the third superconducting material with the second electrically-conductive layer of the second substrate.
12. The method of claim 9 , wherein the third superconducting material comprises indium.